Re: [PATCH v2 1/2] mtd: spi-nor: core: add flag for doing optional SFDP

["Michael Walle" <mwalle@kernel.org>]

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On Thu Jun 6, 2024 at 4:52 PM CEST, Tudor Ambarus wrote:
> On 6/6/24 14:59, Michael Walle wrote:
> > On Thu Jun 6, 2024 at 3:31 PM CEST, Tudor Ambarus wrote:
> >> On 6/3/24 14:09, Esben Haabendal wrote:
> >>> A dedicated flag for triggering call to
> >>> spi_nor_sfdp_init_params_deprecated() allows enabling optional SFDP read
> >>> and parse, with fallback to legacy flash parameters, without having dual,
> >>> quad or octal parameters set in the legacy flash parameters.
> >>>
> >>> With this, spi-nor flash parts without SFDP that is replaced with a
> >>> different flash NOR flash part that does have SFDP, but shares the same
> >>> manufacturer and device ID is easily handled.
> >>>
> >>> Signed-off-by: Esben Haabendal <esben@geanix.com>
> >>> ---
> >>>  drivers/mtd/spi-nor/core.c | 3 ++-
> >>>  drivers/mtd/spi-nor/core.h | 1 +
> >>>  2 files changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> >>> index 3e1f1913536b..1c4d66fc993b 100644
> >>> --- a/drivers/mtd/spi-nor/core.c
> >>> +++ b/drivers/mtd/spi-nor/core.c
> >>> @@ -2933,7 +2933,8 @@ static void spi_nor_init_params_deprecated(struct spi_nor *nor)
> >>>  
> >>>  	spi_nor_manufacturer_init_params(nor);
> >>>  
> >>> -	if (nor->info->no_sfdp_flags & (SPI_NOR_DUAL_READ |
> >>> +	if (nor->info->no_sfdp_flags & (SPI_NOR_TRY_SFDP |
> >>
> >> I don't like that we update deprecated methods. The solution though is
> >> elegant.
> > 
> > I actually had the same concern. But currently there is no
> > non-deprecated way to handle this case, right?
> > 
> > Right now we have the following cases:
> >  (1) pure SFDP parsing
> >  (2) non-SFDP flashes with static configuration only
> >  (3) legacy implementation, where the magic flags decide whether we
> >      use SFDP
> > 
> > Which case is eventually used depends on the ID of the flash -
> > assuming there will only be IDs which either fall into (1) *or* (2).
> > That assumption is clearly wrong :)
> > 
> > I'd propose a new case in spi_nor_init_params()
> >  (4) try SFDP with a fallback to the static flags from the
> >      flash_info db.
> > 
>
> that's not that bad, but I would avoid doing it if it's not common. You
> also have to update the core a bit, you can't use no_sfdp_flags &
> TRY_SFDP, it's misleading. Does it worth it?

IMHO no_sfdp_flags is the correct place (maybe TRY_SFDP is wrong,
maybe SFDP_FALLBACK?) because the flash is first treated like in
case (2). Then SFDP is tried based on that flag. Is it worth it? I
don't know, Esben is doing the development here ;) So up to him.

> I won't oppose too much, but to me it feels that we're trying to keep
> alive a dead man.

Maybe, but we'd have a readily solution if we face a similar
problem in the future. I'm really not sure, how many flashes there
are, but I think these magic bits (which tells the legacy
implementation to try SFDP) will mask quite a few of these.
I.e. in an ideal world where we could finally drop case (3) and
you'd need to split the flashes between case (1) or (2), I think
there will be quite some in (4).

-michael

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